Microstructure and mechanical properties of TiAl/TiAl joints brazed with a newly developed Ti–Ni–Nb–Zr quaternary filler alloy

A novel Ti-Ni-Nb-Zr quaternary filler alloy with the composition of Ti-(19～25)Ni-(15～25)(Nb+Zr)(wt.%) was designed.The filler alloy was composed of(Ti,Nb)ss,(Ti,Zr,Nb)ss+(Ti,Zr)₂Ni,α-Ti and Ti₂Ni phases.It was fabricated into filler foil with a thickness of about 45 μm by a rapid solidification technique.The results indicate that the liquidus temperature of the Ti-Ni-Nb-Zr brazing alloy was about 978℃,and the brazing alloy presented excellent wettability on TiAl substrate.T...     

Microstructure evolution and mechanical properties of Ti_2AlNb/TiAl brazed joint using newly-developed Ti–Ni–Nb–Zr filler alloy

Joining of Ti_2AlNb alloy to TiAl intermetallics was conducted by the newly-developed Ti–Ni–Nb–Zr brazing filler alloy.The microstructure evolution of the joints was investigated by scanning electron microscope (SEM),energy dispersive spectrometer (EDS) and electron backscatter diffraction (EBSD).The macro-micro mechanical properties were studied by shear test and nano-indentation test.Typical interfacial microstructures across the brazing seam were Ti_2AlNb substrate,α_2-Ti_3Al+β-Ti,γ-TiAl+Ti_2Ni+TiNi+α_2-Ti_3Al,α_2-Ti_3Al+β-Ti,TiAl substrate.The Ti_2Ni phase were firstly dissolved in the joints brazed at 1000°C for 10 min and then precipitated after a prolonged holding time of 15 min.The nano-indentation test revealed that Ti_2Ni phase exhibited the highest hardness of 12.60 GPa.The joints brazed at 1000°C/15 min presented the maximum shear strength of271 MPa.The dissolution and precipitation behavior of Ti_2Ni phase was also discussed.     

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al-17Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al-17Si-1Fe alloys only contained a long, needle-shaped β-Al₅FeSi phase at 0 MPa. In addition to the β-Al₅FeSi phase, the HPSC Al-17Si-1.5Fe alloy also contained the plate-shaped δ-Al₄FeSi₂ phase. A fine, block-shaped δ-Al₄FeSi₂ phase was formed in the Al-17Si-1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17Si-1Fe alloy formed by HPSC exceeded that of the Al-17Si-1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17Si-1Fe alloy formed by HPRC decreased to a value lower than that of the Al-17Si-1.5Fe alloy formed in the same manner.     

Microstructure and property of the Ti-24Al-15Nb-1.5Mo/TC11 joint welded by electron beam welding

The Ti-24Al-15Nb-1.5Mo alloy, in the as-forged and heat-treated states, was joined to the as-forged TC 11 titanium alloy by electron beam welding with the heat inputs of 135 and 150 kJ/m. Then the microstructure and property of the Ti-24Al-15Nb-1.5Mo/TC 11 welding interface were investigated. The results show that the phase constitution of the weld is not related to the heat input, and is mainly composed of α' phase. Moreover, the intermetallic phases of TiEAlNb, MoNb, Nb₃Al, and TiAl₃ are formed in the weld zone. Therefore, the microhardness value of the weld zone is higher than that of the other portions in the same sample. The profile of the weld is asymmetrically fimnel-like. The grain sizes of the weld and its heat-affected zones are increased with increasing heat input. There is an obvious difference in the element content of the welding interface; only the alloying elements in the fusion zone reach a new balance during solidification.     

High-throughput synthesis of oxidation-resistant Nb–Si based alloy thin film by magnetron co-sputtering

A high-throughput method was applied to study oxidation behavior of Nb-Si based alloy using composition spread alloy film as combinatorial libraries.An extended range of composition gradients of Nb-Si based alloy film was deposited by(multi)magnetron co-sputtering.The as-deposited film was composed of amorphous phase.Cr₂ Nb,Nb₅ Si₃ and Nbss could be detected after annealing treatment.After oxidation at 1250℃ for 10 min and 20 min,the film composition space was di...     

A Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous filler metal for improving the strength of Ti–6Al–4V alloy brazing joint

Ti_(50)Zr_(27)Cu_8Ni_4Co_3Fe_2Al_3Sn_3(at%) amorphous filler metal with low Cu and Ni contents in a melt-spun ribbon form was developed for improving mechanical properties of Ti–6Al–4V alloy brazing joint through decreasing brittle intermetallics in the braze zone. Investigation on the crystallization behavior of the multicomponent Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous alloy indicates the high stability of the supercooled liquid against crystallization that favors the formation of amorphous structure. The Ti–6Al–4V joint brazed with this Ti-based amorphous filler metal with low total content of Cu and Ni at 1203K for 900s mainly consists of α-Ti, β-Ti,minor Ti–Zr-rich phase and only a small amount of Ti_3Cu intermetallics, leading to the high shear strength of the joint of about 460 MPa. Multicomponent composition design of amorphous alloys is an effective way of tailoring filler metals for improving the joint strength.     

Microstructure and mechanical properties of the SiC/Zr4 joints brazed with TiZrNiCu filler for nuclear application

Si C ceramic has been successfully joined to Zr4 alloy using Ti Zr Ni Cu filler within the temperature range1173 K–1263 K and 15 min holding time. The morphology of the Si C/Zr4 joints was investigated by SEM, and the phases in the joints were characterized by XRD and TEM. The results indicated that part of the Zr4 substrate dissolved into the molten filler during the brazing process, contributed to the increasing Zr content and the formation of Zr[Ti] solid solution in the joints. In addition, β-Ti phase was discovered in the brazing seam. This might be attributed to the existence of β-Ti stable elements, Cu and Ni. The interface characterization showed that Si C reacted with filler alloy during the brazing process, formed a(Zr, Ti)C reaction layer on Si C surface and Zr2 Si compound near Si C substrate. Finally, the mechanical properties of the joints, evaluated by a shear strength test, reached a maximum of 95 MPa at the brazing temperature of 1203 K.     

Improving the tensile properties of extruded Mg–Ga alloy by ageing treatment

A hot-extruded Mg-5Ga alloy was subjected to ageing treatment at 150 ?°C, 190 ?°C and 230 ?°C. The microstructures and mechanical properties of the extruded and aged alloy were examined in this study. Microstructure examinations suggested that particle-shaped and rod-shaped Mg₅Ga₂ were precipitated in the alloy after peak ageing treatment. The extruded alloy showed the yield strength, ultimate tensile strength and elongation to fracture of 157.6 ?MPa, 248.6 ?MPa and 17.5%, respectively. After peak ageing, the yield strength and ultimate tensile strength can be enhanced by as much as 15.7% and 8.6% reaching 182.3 ?MPa and 270 ?MPa, respectively. The improvement of the tensile strengths is mainly attributed to the enhanced precipitation strengthening by newly formed fine Mg₅Ga₂ precipitates. The ductility of the alloy was slightly increased by peak ageing at low temperatures (150 ?°C and 190 ?°C), but remarkably decreased by peak ageing at high temperature (230 ?°C) due to the formation of coarsened Mg₅Ga₂ particles which easily initiated the cracks during tensile deformation.     

Optimization of mechanical properties of Sn-3.8Ag-0.7Cu alloys by the additions of Bi,In and Ti

Bi, In and Ti were added to Sn-3.8Ag-0.7Cu (SAC387) solder alloy to optimize the mechanical performance. The alloying effects of Bi, In and Ti on the microstructure, thermal and mechanical properties of SAC387 based solder alloys were investigated. The results demonstrate that adding 3.5 ?wt % of Bi could refine the microstructure, optimize the thermal properties, and improve the tensile strength. Meanwhile, the ductility of the solder alloys reduced evidently. Adding 2.8 ?wt % of In into SAC387–3.5 ?wt %Bi alloy could increase both the strength and ductility, which is attributed to the beneficial effect of In addition, as adding In could improve the solubility of Bi in the β-Sn matrix. Meanwhile, the melting point was reduced, and the wettability improved with the addition of In. Introducing amounts of Ti into SAC387–3.5 ?wt % Bi-2.8 ?wt % In alloy could further increase the strength. However, the ductility was significantly reduced when 0.8 ?wt % of Ti was added due to the formation of the coarse Ti₂Sn₃ phase. The undercooling was remarkably reduced with the addition of Ti. The nanoindentation tests demonstrate that the hardness increased mainly due to the hardening effect of the Bi addition. Among all the samples prepared, alloy SAC387–3.5 ?wt % Bi exhibited the highest creep resistance at the ambient temperature. Further adding In and Ti into SAC387–3.5 ?wt % Bi alloys reduced the creep resistance of the solder alloys. The mechanism associated with the different mechanical responses is also discussed in this study.     

Hydrogen absorption-desorption characteristic of (Ti0.85Zr0.15)1.1Cr1-xMoxMn based alloys with C14 Laves phase

The microstructure and hydrogen absorption-desorption characteristic of (Ti_0.85Zr_0.15)_1.1Cr_1-xMo_xMn (x ?= ?0.05, 0.1, 0.15, 0.2 ?at.%) alloys were investigated. The results showed that the corresponding alloys were determined as a single phase of C14-type Laves structure. With the increase of Mo content, the maximum and reversible hydrogen absorption capacity decreased, the slope factor H_f increased. Among the studied alloys, (Ti_0.85Zr_0.15)_1.1Cr_0.95Mo_0.05Mn had the best overall properties for practical application of hydrogen storage materials. The maximum and reversible hydrogen storage capacity were 1.76 ?wt% and 1.09 ?wt%, the slope factor H_f was 0.51, and its dissociation enthalpy (ΔH_d) and entropy change (ΔS_d) were 23.1 ?kJ ?mol^?1H₂, 93.8J ?K^?1mol^?1H₂ at 303K, respectively. By studying the dissociation pressures of the synthesized metal hydrides, it was found that Mo had a special effect on the dissociation pressure of Ti–Zr–Cr–Mo–Mn alloys. Among the four alloys, (Ti_0.85Zr_0.15)_1.1Cr_0.95Mo_0.05Mn alloy had the largest hydrogen absorption capacity and the fastest hydrogen desorption rate, which can meet the commercialization demand of hydrogen fuel cell hydrogen supply system.     

Effect of long-term aging treatment on the tensile strength and ductility of GH 605 superalloy

Aging treatment is an effective way to optimize the mechanical properties of Co-based superalloys. In this study, commercial GH 605 superalloy was subjected to aging treatment at 650 ?°C in a wide time range up to 1000 ?h. The effects of aging time on the tensile characteristics, microstructure evolution and mechanical properties were systematically investigated at room temperature (RT) and 900 ?°C. The results showed that the volume fractions of M₆C and M₂₃C₆ carbide increased with the aging time. After long-term aging treatment, the yield strength (YS) at RT was enhanced from 490.3 ?MPa to 805.9 ?MPa, while the alloy still had high tensile ductility (above 20%). Microscopic observations by transmission electron microscopy (TEM) indicated that the strengthening mechanism was related to carbide precipitation inside the grains and the change in the dislocation slipping mode. Moreover, long-term aging treatment can increase the elongation from 24.1% to 47.3% at 900 ?°C accompanied by a slight increase of YS from 299.3 ?MPa to 313.9 ?MPa. Based on detailed microstructure analysis the strengthening mechanism can be attributed to the refined grains as well as carbide precipitation inside the grains and around the grain boundaries.     

Influence of modulation period for β-Cu2+xSe/SiC nano-multilayer films on their thermoelectric properties

In this study, β-Cu_2+xSe/SiC nano-multilayer films with different modulation period were successfully deposited on SiO₂/Si substrates by sputtering alternately using Cu–Se and SiC targets. The deposited films were observed on both surface and cross-section, and the thermoelectric properties were studied. The results show that both carrier concentration and mobility at room temperature decreased with the reducing modulation period for the nano-multilayer films. The conductivity slightly decreased and Seebeck coefficient greatly increased with the reducing modulation period. As a result of competition, the power factor of the nano multilayer films increased with the reducing modulation period because the positive effect of the Seebeck coefficient exceeded the negative effect of the conductivity. In the case of β-Cu_2+xSe/SiC nano multilayer film with the smallest modulation periods (210 ?nm), the power factor reached 0.39 ?mWm^?1K^?2 and 0.59 ?mWm^?1K^?2 at room temperature and 325 ?°C, respectively. The enhanced power factor for nano multilayer films is attributed to the scattering process at the β-Cu_2+xSe/SiC layer interface, which reduces the carrier concentration and the mobility. It is concluded that the thermoelectric properties of β-Cu_2+xSe films can be effectively improved by designing nano multilayer structure.     

Microstructure s and mechanical properties of Ti3Al/Ni-based superalloy joints arc welded with Ti –Nb and Ti– Ni – Nb filler alloys

Dissimilar joining of Ti3Al-based alloy to Ni-based superalloy has been carried out using gas tungsten arc(GTA) welding technology with Ti–Nb and Ti–Ni–Nb filler alloys.The joint welded with the Ti–Nb filler alloy contained much less interfacial brittle phases than the one using the Ti–Ni–Nb filler alloy.The average room-temperature tensile strength of the joint welded with Ti–Nb was 202 MPa and the strength value of the one welded with Ti–Ni–Nb was 128 MPa.For both fillers,the weak links of the dissimilar joints were the weld/In718 interfaces.The presence of TiNi,TiNi3 and Ni3Nb intermetallic compounds in the joint welded with Ti–Ni–Nb induced microcracks at the weld/In718 interface and deteriorated the mechanical properties of the joint.And the adoption of the Ti–Nb filler alloy decreased the formation tendency of interfacial brittle phases to some extent and thus enhanced the tensile strength of the joint.     

The microstructure evolution and phase transformation behavior of a β-solidifying γ-TiAl alloy during creep

The microstructural evolution and creep behavior of the Ti-43.5Al–4Nb–1Mo-0.1B alloy have been investigated by scanning electron microscope(SEM) and transmission electron microscope(TEM). The excellent creep property was obtained with a fully lamellar(FL) microstructure containing the least grain boundary β_o phase(GB-β_o).TEM results revealed that after creep testing the α₂→βophase transformation was observed in the FL microstructure. The formation βophase is asso...     

Effect of Ce addition on hot corrosion behaviours of a cast γ′-strengthened Co–Al–W–Mo–Ta–B alloy at 800 ​°C

Hot corrosion behaviours of a novel Co–9Al-4.5W-4.5Mo–2Ta-0.02B alloy doped with 0.01, 0.05, 0.1 and 0.2 ?at% Ce exposed at 800 ?°C in a solution of 75%Na₂SO₄/25%NaCl were investigated. The alloys comprised a coherent γ-Co_SS/γ′-Co₃(Al, W) microstructure (0.01Ce and 0.05Ce alloys) and κ-Co₃(W, Mo) precipitates (0.1Ce and 0.2Ce alloys) at grain boundaries. Hot corrosion kinetics curves demonstrated the parabolic time dependency profile with two stages: the first parabolic stage is within the beginning ～50 ?h corrosion and follows by the second parabolic stage. With an increasing nominal Ce content the weight gain of the alloy significantly decreased from approximately 70.1 ?mg ?cm^?2 (0.01Ce) to 40.8 ?mg ?cm^?2 (0.2Ce) when exposed for 100 ?h. A two-layer corrosion scale formed, and the scale was composed of an outer layer of Co₃O₄ oxide with spinel compounds of CoAl₂O₄, CoWO₄and CoSO₄, and an inner γ/needle-like Co₃W/sulphide layer adhered to the substrate. Heavy spallation of the corrosion scale occurred in the 0.01Ce～0.1Ce alloys, however, spallation was slight in the 0.2Ce alloy. The excellent corrosion resistance of the 0.2Ce alloy could be attributed mainly to the formation of continuous Al₂O₃ lines in the corrosion scale, as well as the prolongation of the incubation period of the corrosion product spallation.     

The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al-Mg2Si in situ composites

The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al-Mg₂Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al-Mg₂Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg₂Si particles (from 28 to 12 μm), the spacing of eutectic Mg₂Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg₂Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg₂Si phase and the grains in the Al-Mg₂Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al-Mg₂Si composites and AA6061 alloy billets.     

Microstructure and wear behavior of Mo–60Si–5B coating doped with 0.5 ​at% La by spark plasma sintering

Mo–60Si–5B coating doped with 0.5 ?at% La was prepared on niobium silicon based alloy by spark plasma sintering. The microstructure and wear behavior of the 0.5La–Mo–60Si–5B (0.5La-MSB) coating were investigated. The results show that the mean grain sizes of the Mo–60Si–5B (0La-MSB) and 0.5La-MSB coatings are calculated to be 3.27 ?μm and 2.85 ?μm, respectively. The addition of La plays a role of refining the grains of 0.5La-MSB coating. The specific wear rate of 0.5La-MSB coating is decreased by up to 26.8% at the oscillation frequency of 20 ?Hz and the sliding load of 11 ?N compared to 0La-MSB coating. The anti-friction performance of Mo–60Si–5B coating is modified by the addition of 0.5 ?at.% La. The improvement of anti-friction performance of the Mo–60Si–5B coating is due to the increased hardness and the provided lubrication function by La₂O₃.     

Rapid directionally solidified microstructure characteristic and fracture behaviour of laser melting deposited Nb–Si–Ti alloy

Aiming at achieving fine and directionally-solidified microstructure of Nb-Si based alloy,Nb,Si and Ti powder particles were utilized as the raw materials,and laser melting deposition(LMD) experiments were conducted with1500 W and 2000 W laser power,respectively.The microstructure characteristic,micro-hardness,and indentation fracture toughness were examined by scanning electron microscope(SEM),X-ray energy dispersive spectrometer(XEDS) and X-ray diffraction(XRD).The results showed that the two ...     

Effects of Sb and heat treatment on the microstructure of Al-15.5wt%Mg2Si alloy

The modification effects of alloying element Sb and heat treatment on Al-15.5wt%Mg₂Si alloy were investigated by Olympus microscopy (OM), scanning electron microscopy and energy disperse spectroscopy (SEM-EDS), and X-ray diffraction (XRD). It is found that Sb plays a significant role in shaping primary Mg₂Si phase and eutectic Mg₂Si phase in Al-15.5wt%Mg₂Si alloy. The Sb addition of about 1.0wt% makes the resultant alloy show the finest primary Mg₂Si phase and the eutectic Mg₂Si phase with well distribution. But further increasing the Sb content decreases the amount of primary Mg₂Si phase, and some segregated phases appear at regions between the grains. In addition, heat treatment can modify the microstructural feature of Sb-modified Al-15.5wt%Mg₂Si alloy in terms of obviously shortening the nodulizing time of primary Mg₂Si phase and eutectic Mg₂Si phase.     

Reversible hydrogenation of AB2-type Zr–Mg–Ni–V based hydrogen storage alloys

The development of hydrogen energy is hindered by the lack of high-efficiency hydrogen storage materials. To explore new high-capacity hydrogen storage alloys, reversible hydrogen storage in AB₂-type alloy is realized by using A or B-side elemental substitution. The substitution of small atomic-radius element Zr and Mg on A-side of YNi₂ and partial substitution of large atomic-radius element V on B-side of YNi₂ alloy was investigated in this study. The obtained ZrMgNi₄, ZrMgNi₃V, and ZrMgNi₂V₂ alloys remained single Laves phase structure at as-annealed, hydrogenated and dehydrogenated states, indicating that the hydrogen-induced amorphization and disproportionation was eliminated. From ZrMgNi₄ to ZrMgNi₂V₂ with the increase of the degree of vanadium substitution, the reversible hydrogen storage capacity increased from 0.6 ?wt% (0.35H/M) to 1.8 ?wt% (1.0H/M), meanwhile the lattice stability gradually increased. The ZrMgNi₂V₂ alloy could absorb 1.8 ?wt% hydrogen in about 2 ?h ?at 300 ?K under 4 ?MPa H₂ pressure and reversibly desorb the absorbed hydrogen in approximately 30 ?min ?at 473 ?K without complicated activation process. The prominent properties of ZrMgNi₂V₂ elucidate its high potential for hydrogen storage application.